Compressor and the like



Oct. 10, 1933. J, HOLLOWAY 1 1,930,011

COMPRESSOR AND THE LIKE I Filed Jan. 21. 1932 2 Sheets-Sheet l 3 I'll IIIIIIIIIIIIIIIIIIIIIIII J J, H 01/ a y Patented Oct. 10, 1933 UNITED STATES COMPRESSOR AND THE LIKE John Holloway, Burnham, England, assignor of one-half to. Thos W. Ward Limiteishefiield,

England Application January 21, 1932, Serial. No. 588,018, andiin Great Britain September 9, 1931 I 11 Claims. (o1. 230-180) This invention relates to air or other fluid compressors or pumps of" the type wherein a plurality of pistons are arranged to operate in a commoncylinder or'casing and are caused to approach each other while moving in the same direction during a power or compression stroke.

"According to' a1prior proposal, a mechanism of the above type has been applied to an air compressor in which twopistons adapted to compress air betweenthem were connected to spaced points on a rocking member in such a way that at the end'of the compression stroke the pistons assumed a locked or perfectly balanced condition, due to the arms of the rocking member having equal leverage. p

This invention consists in an air or other fluid compressor orjpump'in which a pair of piston members'having difierent'strokes are reciprocated in a cylinder to compress the fluid between them, characterized by the provision of two stages of compression in a single cylinder by performing a preliminary compression between one of the' piston members and an end cover of the cylinder while the second stage of compression is performed between two piston members which iii-addition are so connected to a driving member or members that the opposed forces on the pistons are brought substantially, but preferably not completely, into balance at the end of the stroke, in other words the opposed forces are balanced through the driving member which interconnects thepistons. A common oscillating or revolving drive element may be provided for the pistons and so arranged as to exert unequal or predetermined leverages thereon when the two pistons are at the end of their stroke. 7 Both ends of the cylinder maybe closed by covers and air compressed in one of the chambers so formed may be delivered through a spring loaded valve to the suction side of the other piston to give a supercharging effect, or the air compressed in such chamber may be used as part of the first stage compression in which case the air is led to the intercooler chamber before entering the second stage part of thecylinder.

Other features of the invention will be apparentfrom the following description and claims. "Referring to'the accompanying drawings? Figure 1 is a sectional elevation of a two-stage by way of example to a two-stage air compressor,

a cylinder 1 is supported on -a suitable frame '2 and is-providedwith two pistons 3 and 4 between which the air may be compressed. Movement is imparted to the pistons by means of anoscillatory driving member comprising a pair of arms 5 and 6 attached to a hub oscillating about a' shaft '7 on a ball or roller bearing 8. In this example the arms make an angle of about 63 withtheir vertex, but this may be varied if desired. The longer arm 5 is'connected by means of a short link 9110 the pin 10 of a crosshead 11 slidable 'in' guides 12, the crosshead being preferably of piston form and connected by means of a piston rod'13 to "the lower piston 4. The shorter arm -6 is connected n A by means of a long link 14 to the upper piston3, 7 the pin 15 of which" projects laterally through a suitable slot 16 in the cylinder walls. Thevarious and links'are preferably duplicated on opposite sides of the cross-head to give syinmet rical reactions. Withthe parts in the position shown, the two pistons being at the end of their upward stroke, the arm 5 makes an angle of about 30 with the horizontal. -When the pistons are at their maximum-distance apart, i. e." at the-beginning of the working stroke, theshorter arm'6 30 is some few degrees beyond'the vertical as-indicated by the point 17 in'Figurel. Power "from any suitable source, such as'an electric motor for example, isapplied to the compressor through a shaft 18 and crank 19 which is connected to the 8 crosshead l1 by a connecting rod20 and it will be seen that with the piston 4in its lowest position, rotation of the crank 19 will cause the pistons 3 and; to move in the same direction but at different velocities, the piston 4' overtaking the upperpiston 3 until the parts reach the position iii-which they are shown in Figure 1. 'At or near this position the links 9 and 14 will be pulling in o'pposite'directions on the ends of the c'rankarms 5"and 6 'byreason of the pressure of the air or other fluid compressed between the pistons. Since the arms are of unequal lengths the force exerted by thecompressedfluid will be partially balanced but a small out-'of-balance forcewill remain, the purpose of which will be explained hereinafter; Y

The lower end of the cylinder 1 is closed by a cover 21 which may be provided with a suitable gland for the piston rod 13. Both the cylinder and cover are'water-jacketed as shown.

Air is preferably admitted on the upward (suction) stroke of the piston 4 at '22 and'passes through an'inlet valve 23 andan inlet'port'24 to the lower end of the cylinder. On the downward stroke of the'pistonthe airis discharged through 24 to a discharge valve 25 and thence passes through a passage 26 which is waterjacketed and afterwards passes through the second-stage inlet valve 27 to the space between the pistons by way of the port 28. On the following upward stroke of the piston 4 a final stage of compression is performed between the two piswhich may be utilized to resist the momentum of the moving masses and assist in their reversal and return. It is foundthat by providing a slight differential balance in this way the efficiency and general running of the compressor is greatly improved. Moreover, the particular inclination chosen for the arms gives a dwell or nearly dead period for thepiston 4 when the arm 6 is in the neighbourhood-of the point 17 and this arrangement enables the overall length of the cylinder to be reduced. It will be readily seen that by varying theangle between the crank arms 5 and 6 it is possible to obtain different ratios between the first. and second stage cylinder volumes, thus obtaining a practically uniform crank effort throughout the cycle of operations.

A modified form of driving mechanism for a compressor of the general type described. above is shown in Figure 2, where 3 and 4 are two pistons working in a common cylinder and adapted to compress air or other fluid between them. The piston 4 carries a rod 13 attached to a crosshead 43 in which is seated a pin 44. A slotted arm 45 pivoted at 46 to the frame of the compressor engages the pin 44. v The arm 45 is rigidly attached to a second arm 4''! provided with a long slot 48, the angle between the two arms being in this instance about 30. The upper piston 3 is connected by a link or links 14 to a pin 39 sliding in the slot 48 and this pin is also connected by means of a link 49 to a fixed pivot 50 on the frame.

e The arrangement of the various members is such that when both pistons are together, i. e. in the position shown in Figure 2 which is the point of maximum compression, both crank arms are preferably upwardly inclined with respect to a horizontal plane passing through the fixed pivot 46. The drive may be imparted to the crosshead 43 in any convenient manner as by a crank 19 and connecting rod 20, and it will be seen that on a partial rotation of the double-armed crank 45, 47 the lower piston 4 will be moved through a distance determined by the radius of the arm 45. The arm 47 will move through the same angle, but by reason of the pin 39 being constrained by the link 49 it will traverse the slot 48 and thus the piston 3 will be actuated by an arm of progressively decreasing radius with the result that the upper piston will not move so far as the lower. On the compression stroke these movements will take place in the reverse order and the air will be compressed between the two pistons, there being a partial balance at least of the pistons when the point of maximum compression is reached.

v The variation in the effective length of one of the lever arms during the stroke by the means described above enables a comparatively large range of compression ratios to be obtained. Like wise it also allows a variable rate of movement to be obtained between the two pistons and the forces operating on each piston to be brought into balance at any desired part of the stroke by suitably varying the position of the fixed pivot 50.

In the present example the upper end of the cylinder 1 is closed and may be employed to effect a preliminary compression of air for supercharging purposes or when desired to effect a first stage compression similar to that obtained on the lower side of the lower piston. In the former case in its simplest form the upper piston has a recess and a cover 53 is fitted to the upper end of the cylinder and is provided with a light spring loaded inlet valve 54 and a pipe connection 55 leading to the lower cylinder chamber by way ofa nonreturn valve 57 which is spring loaded to open at a determined pressure. On the downward stroke of the piston 3 air is drawn in through the valve 54 and on the return stroke of the piston, when the lower piston is causing air to be drawn into the space beneath it, the ,air in the space 1& above the upper piston is compressed and, at a determined time during the stroke, is discharged under pressure through the valve 51 to supplement the air already drawn into the space beneath the lower piston. In this way the volu- 1,05

metric efliciency of the compressor is improved and in addition a cushioning effect is obtained at the end of the power stroke. 7 7

It will be understood that the invention is. not confined to compressors or pumps having k1!) two stages of compression only.

Having now described my invention, what I claim as new and desire to secure by Letters Patent is:- I 1. A compressor or pump comprising a cylin-. 1(1 der, a pair of piston members reciprocable therein, drive means for causing said piston members to move in the'same direction at different speeds during each stroke so that they alternately approach and recede from each other, means for 9 admitting fluid for compression between a piston member and an end of the cylinder and means for transferring the compressed fluid to the space betweenthe piston membersforfurther compression, said drive means being adapted to effect 25 a substantial balance of the opposed forces on the piston members when compression between them is completed.

v 2. A compressor or pump comprising a cylinder, a pair of pistons therein, drive means for '39 reciprocating said pistons in the same direction at different speeds so that they alternately ap-' proach and recede from each other, means for. admitting fluid to be compressed betweena piston and a cylinder end and means for trans- 3.5 ferring the compressed fluid to the space between the pistons for further compression, said drive means being adapted to effect a substantial but not complete balance of the opposed forces on the pistons when compression between them is 0 completed.

3. A compressor or pump comprising a casing, a pair of piston members reciprocable therein, drive means for causing said piston members to move in the same direction at different speeds 4: during each stroke so that they alternately approach and recede from each other, said drive means comprising an oscillatable pivoted element, to which the piston members are connected at spaced points by links, means for admitting 9 fluid to the chamber formed between a piston member and an end of the casing to be compressed therein when said piston member appoaches said casing end, and means for transferring fluid so compressed to the space between the piston members to be further compressed when said piston members approach one another, said drive element being so arranged that the forces acting thereon due to the pressure between the pistons at the end of the compression stroke between them are in substantially balanced opposition.

4. A compressor or pump comprising a-cylinder, a pair of pistons therein, drive means for reciprocating said pistons in the same direction at different speeds so that they alternately approach and recede from each other, means for admitting fluid to be compressed between a piston and a cylinder end and means for transferring the compressed fluid to the space between the pistons for further compression, said drive means being adapted to effect a substantial but not complete balance of the opposed forces on the pistons when compression betweenthem is completed, the out-of-balance force which then remains being utilized to assist in the return of the reciprocating masses.

5. A compressor or pump comprising a casing, a pair of piston members reciprocable therein, drive means for causing said piston members to move in the same direction at different speeds during each stroke so that they alternately approach and recede from each other, said drive means comprising an oscillatable pivoted element, to which the piston members are connected at spaced points by links, means for admitting fluid to the chamber formed between a piston member and an end of the casing to be compressed therein when said piston member approaches said casing end, and means for transferring fluid so compressed to the space between the piston members to be further compressed when said piston members approach one another, said drive element being so arranged that the forces acting thereon due to the pressure between the pistons at the end of the compression stroke between them are in substantially balanced opposition but have a resultant out-ofbalance force which is utilized to effect the return of the reciprocating masses.

6. A compressor or pump comprising a cylinder, a pair of piston members reciprocable therein, lever elements connected to the piston members and operable to cause said members to move in the same direction at different speeds during each stroke so that the piston members alternately approach and recede from each other to compress fluid between them, said lever elements being so arranged that the opposed forces on the piston members are substantially balanced when compression between them is completed, and means for varying the effective length of one of said lever elements during the stroke.

7. In a compressor or pump the combination comprising a cylinder, a pair of pistons therein, a pivoted arm connected to one of said pistons for reciprocating the piston, a slotted second arm fixed to said first arm, a pin slidable in the slot in said second arm, a connection between said pin and the other of said pistons, and means for varying the position of said pin in the slot during the strokes of the pistons whereby the effective length of one of the lever arms is varied.

8. In a compressor or pumpthe combination comprising a cylinder, a pair of pistons therein, a pivoted arm connected to one of said pistons for reciprocating the same, a slotted second arm fixed to said first arm, a pin slidable in the slot in said second arm, a connection between said pin and the other of said pistons and a pivoted link connecting said pin to a fixed pivot on'the frame whereby the position of the pin in the slot is varied during the stroke of the respective piston.

9. In a compressor or pump the combination comprising a cylinder, a pair of pistons therein, a drive element interconnecting such pistons and adapted to cause the pistons to move in the same direction at different speeds to compress fluid between them and to bring said pistons into substantial but not necessarily complete balance at the end of the said compression stroke, and means for varying during the stroke the distance between a point on the drive element connected to a piston and the center of rotation of said element.

10. A compressor comprising a cylinder, a pair of piston members reciprocable therein, drive means for causing said piston members to move in the same direction at different speeds during each stroke so that they alternately approach and recede from each other, means for admitting fluid for compression between a piston member and one end of the cylinder, means for admitting fluid for compression between a piston member. and the other end of the cylinder, means for transferring the fluid compressed at one end of the cylinder to the opposite end to supercharge the fluid already in said cylinder prior to compression thereof and means for transferring the fluid after compression to the space between the pistons for further compression. 1 g

11. In a compressor the combination comprising a cylinder closed at both ends, a pair of pis- 120 tons reciprocable therein, drive means for causing said piston members to move in the same direction at different speeds during each stroke so that they alternately approach and recede to and from each other and the respective ends of the cylinder, an inlet valve controlling the admission of air to one end of the cylinder, a discharge valve controlling the discharge of air from said end of the cylinder to a conduit, a second inlet valve controlling the admission of 130 compressed air from said conduit to the cylinder in the space between the two pistons, a second discharge valve controlling the discharge from said space to the delivery line, an inlet valve controlling admission of air to the oppositeend 135 of the cylinder, a connection between said end of the cylinder and the first-mentioned end thereof and a spring-loaded valve controlling the delivery of compressed air through said connection to said first-mentioned end of the cylinder 140 for supercharging purposes.

7 JOHN HOLLOWAY. 

